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          25.函数编程
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              <time title="创建时间：2020-06-27 07:31:41 / 修改时间：15:31:55" itemprop="dateCreated datePublished" datetime="2020-06-27T07:31:41+08:00">2020-06-27</time>
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        <p>多分支if语句<br>if ；then<br>elif ；then<br>。。。<br>else<br>fi</p>
<p>case 语句：</p>
<p>示例1：显示一个菜单给用户<br>cpu）display cpu information<br>mem)meminfo<br>disk) diskinfo<br>quit) quit</p>
<p>要求：</p>
<ol>
<li>提示用户给出自己的选择</li>
<li>正确的选择给出相应的信息；否则，提示重新选择正确的选项；</li>
</ol>
<p>case $VARAIBLE in<br>PAT1)<br>    分支1<br>    ;;<br>PAT2)<br>    分支2<br>    ;;<br>PAT3)<br>    …<br>    …<br>*)<br>    分支n<br>    ;;<br>esac</p>
<p>示例：写一个服务框架脚本</p>
<ol>
<li>此脚本可接受start stop restart status 四个参数之一</li>
<li>如果参数非4者，提示帮助后退出</li>
<li>start，则创建lockfile，并显示启动完成；stop，删除lockfile，并显示停止；restart，先删除在创建，而后显示重启完成，status，判断文件是否存在，存在，显示running，不存在显示stopped；</li>
</ol>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line">#!&#x2F;bin&#x2F;bash</span><br><span class="line">#</span><br><span class="line">prog&#x3D;$(basename $0)</span><br><span class="line">lockfile&#x3D;&#x2F;var&#x2F;lock&#x2F;subsys&#x2F;$prog</span><br><span class="line"></span><br><span class="line">case $1 in</span><br><span class="line">start)</span><br><span class="line">    if [ -f $lockfile ]; then</span><br><span class="line">        echo &quot;$prog is Running.&quot;</span><br><span class="line">    else</span><br><span class="line">        touch $lockfile</span><br><span class="line">        [ $? -eq 0 ] &amp;&amp; echo &quot;start $prog finished.&quot;</span><br><span class="line">    fi  </span><br><span class="line">    ;;  </span><br><span class="line">stop)</span><br><span class="line">    if [ -f $lockfile ]; then</span><br><span class="line">        rm -f $lockfile</span><br><span class="line">        [ $? -eq 0 ] &amp;&amp; echo &quot;stop $prog finished.&quot;</span><br><span class="line">    else</span><br><span class="line">        echo &quot;$prog stopped.&quot;</span><br><span class="line">    fi  </span><br><span class="line">    ;;  </span><br><span class="line">restart)</span><br><span class="line">    if [ -f $lockfile ]; then</span><br><span class="line">        rm -f $lockfile</span><br><span class="line">        touch $lockfile</span><br><span class="line">        echo &quot;Restarting finished.&quot;</span><br><span class="line">    else</span><br><span class="line">        touch -f $lockfile</span><br><span class="line">        echo &quot;start $prog finished.&quot;</span><br><span class="line">    fi  </span><br><span class="line">    ;;  </span><br><span class="line">status)</span><br><span class="line">    if [ -f $lockfile ]; then</span><br><span class="line">        echo &quot;Running.&quot;</span><br><span class="line">    else</span><br><span class="line">        echo &quot;Stopped.&quot;</span><br><span class="line">    fi  </span><br><span class="line">    ;;</span><br><span class="line">*)</span><br><span class="line">    echo &quot;Usage:$0 start|stop|restart|status.&quot;</span><br><span class="line">    exit 1</span><br><span class="line">esac</span><br></pre></td></tr></table></figure>

<p>函数：function<br>过程式编程：代码重用<br>模块化编程<br>结构化编程</p>
<p>把一段独立功能的代码当做一个整体，并为之一个名字，命名的代码段，此即为函数；</p>
<p>注意：定义函数的代码段不会自动执行，在调用时执行；所谓调用函数；在代码中给定函数名即可；<br>函数名出现的任何位置，在代码执行时；都会被自动替换为函数代码；</p>
<p>语法1.<br>    function f_name{<br>        …函数体…<br>    }<br>语法2.<br>    f_name{<br>        …函数体…<br>    }</p>
<p>函数的声明周期：每次被调用时创建，返回时终止；<br>其状态返回结果为函数体中运行的最后一条命令的状态结果；<br>自定义状态返回值，需要使用return；<br>retutn [0-255]<br>0：成功<br>255：失败</p>
<p>示例：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"> 1 #!&#x2F;bin&#x2F;bash</span><br><span class="line"> 2 #</span><br><span class="line"> 3 username&#x3D;$1</span><br><span class="line"> 4 userinfo() &#123;</span><br><span class="line"> 5     if id &quot;$username&quot; &amp;&gt; &#x2F;dev&#x2F;null; then</span><br><span class="line"> 6         grep &quot;^$username\&gt;&quot; &#x2F;etc&#x2F;passwd | cut -d: -f3,7</span><br><span class="line"> 7     else</span><br><span class="line"> 8         echo &quot;No such user.&quot;</span><br><span class="line"> 9     fi</span><br><span class="line">10 &#125;</span><br><span class="line">11 </span><br><span class="line">12 username&#x3D;$1</span><br><span class="line">13 userinfo</span><br><span class="line">14 username&#x3D;$2</span><br><span class="line">15 userinfo</span><br></pre></td></tr></table></figure>
<p> 函数返回值：<br> 函数的执行结果返回值；</p>
<ol>
<li>使用echo或printf命令进行输出；</li>
<li>函数体中调用的命令的执行结果；</li>
</ol>
<p>函数的退出状态码：</p>
<ol>
<li>默认取决于函数体中执行的最后一条命令的退出状态码；</li>
<li>自定义：return</li>
</ol>
<p>函数可以传递参数：<br>传递参数给函数：<br>    在函数体当中，可以使用$1,$2…引用传递给函数的参数；<br>    在调用函数时，在函数名后面以空白字符分隔给定参数列表即可，例如，testfunc arg1 arg2 arg3 …</p>
<p>练习：写一个脚本：<br>使用函数实现ping一个主机来测试在线状态；主机地址通过参数传递给函数：、<br>测试172.16.1.1-172.16.67.1</p>
<p>练习2：<br>打印NN乘法表</p>
<p>变量作用域<br>局部变量：作用域是函数的声明周期；在函数结束时被自动销毁<br>定义局部变量的方法：local VARAIBLE=VALUE<br>本地变量：作用域是运行脚本的shell进程的生命周期；因此，其作用范围是当前脚本程序文件；</p>
<p>函数递归：<br>    函数直接或者间接调用自身；<br>    10！=10<em>9！=10</em>9<em>8！=10</em>9<em>8</em>7！=…</p>

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